What about meta description of the site? Should that be the same for the whole site or should I have different ones for each page depending on what the page offers.
That's a good question. I used to think that having a different description for each web page works best but lately I'm noticing alot of web site (and particularly blogs with the same description for every web page) keeping the description consistent throughout the entire site and performing very well for the primary keyphrases. Varying descriptions each webpage will increase your keyphrase dynamicability and enforce more keyphrases somewhat but keeping the description the same for each page may have its advantage (for primary, important keyphrases), I think.
"While accurate meta descriptions can improve clickthrough, they won't impact your ranking within search results." - i.e. they are not used to gather keywords
"Using identical or similar descriptions on every page of a site isn't very helpful when individual pages appear in the web results. In these cases we're less likely to display the boilerplate text. Wherever possible, create descriptions that accurately describe the specific page."
In my own experiences, changing your meta description tags according to the main targeted keywords for the destination page would be a nice practice for ranking more keywords purpose, especially for long tail keywords.
Meta description is still important from ranking perspective in Google. It should not be very lengthy and you can use your keywords or phrases within it. It's better if you can use different meta description for different pages of your site. As Google show it in SERP so you also need to make it a bit eye catchy as well.
The meta tag description according to everything I've read about SEO should match what is on the page. So that if someone is searching specifically for a particular item you have they will be able to find it and the search engines will see your site as having a variety of content.